This invention relates in general to a computing scheme for performing non-radar speed computations in digital radar units having central processing systems comprised of microprocessors. In particular, the computing scheme of the present invention uses the microprocessor of a digital radar unit to automatically compute the speed of a moving vehicle in response to distance information manually provided to the unit and timing information derived in the microprocessor in response to activation and deactivation information manually inputted to the unit.
It is a well established principle of physics that the average speed of a vehicle can be calculated by simply dividing the distance traveled by the vehicle during a particular time interval by the time interval. Utilization of this basic principle by law enforcement officers to compute the speed of moving vehicles has taken many forms including the physical apparatus disclosed in the U.S. Pat. No. 3,276,029 issued to Marshall on Sept. 27, 1966 and entitled "Apparatus for Speed Indication". Typically, the law enforcement officer uses a stopwatch or some other timing device to measure the time it takes the vehicle to travel a known distance. The law enforcement officer then computes the speed of the vehicle by either manually dividing the known distance by the measured time or correlating this information on a chart designed for this purpose. This type of speed computation, however, is undesirable because it is slow and cumbersome to perform and is subject to inaccuracy due to device calibration and officer error.
The present invention, however, eliminates these manual operations and provides a reliable scheme for using the microprocessor of a digital radar unit to automatically perform this type of speed computation in response to information manually introduced to the radar unit. In other words, the computing scheme of the present invention represents an add on feature for digital radar units which include central processing units consisting of programmable microprocessors. An example of such a digital radar unit is disclosed in the commonly owned application for U.S. Letters Patent, Aker, et al. filed simultaneously on Apr. 14, 1978 and bearing Ser. No. 896,376 with this application and entitled "Traffic Radar Device". The teachings of that application are incorporated by reference herein.
The computing scheme of the present invention generally comprises two operating routines designated as the stopwatch routine and the interrupt request routine. The stopwatch routine controls the overall operation of the speed computation while the interrupt request routine causes the microprocessor to act as a precision clock which is capable of measuring elapsed time.
A digital radar unit incorporating the computing scheme of the present invention is arranged to be used in either the radar mode of operation or the non-radar mode of operation with the particular mode of operation being selected by the operator of the unit. To use the computing scheme of the present invention, the unit must be powered on, at this time the microprocessor detects that power is being applied and forces the unit to go into a calibration sequence where the displays are exercised, the time bases are checked against each other for accuracy, the stopwatch computation ability is verified and the thumbwheel switches can be manually tested if desired. Next, the digital radar unit must be placed in the non-radar mode of operation by placing an appropriate switch on the control panel of the unit in what is designated the stopwatch position. The known distance between two referece points is then programmed into the digital radar unit using thumbwheel switches. Thereafter, the law enforcement officer using the radar unit activates the speed computation by depressing the timing switch on the control panel of the radar unit as the vehicle being monitored passes the first reference point. Upon depression of the timing switch, the digital radar unit acts as a precision clock which produces an accurate reading of elapsed time. As the monitored vehicle passes the second reference point, the officer once again depresses the timing switch causing the radar unit to terminate the timing operation and initiate the speed calculation and calibration sequence. The radar unit then scales the speed computation to provide a measurement of speed in terms of miles per hour, kilometers per hour or any other programmed unit of measurement. The speed measurement is then displayed by the radar unit.
Depression of the timing button a third time blanks the radar displays and places the radar unit in condition to perform a second speed computation. Additional features of the present invention include provision of an error indication if a set maximum time period is exceeded or a selected maximum speed is surpassed.
It is therefore an object of the present invention to provide a computing scheme for using a digital radar unit to compute the speed of a moving vehicle in a non-radar manner. This unit would have the ability to be easily changed to allow the display of speed information in various units of measure.
Another object of the present invention is to provide a scheme whereby the unit would automatically check the accuracy of its own system time base prior to displaying any speed information.
Another object of the present invention is to provide a scheme for computing the speed of a moving vehicle in a digital radar unit having a programmable microprocessor in response to information manually inputted to the unit.
A further object of the present invention is to provide a computing scheme which provides added flexibility to a digital radar unit by allowing the radar unit to compute the speed of a moving vehicle in response to information manually inputted to the unit.
It is a further object of the present invention to provide a computing scheme which initiates and terminates the speed computing operating in response to depression of a single timing switch.
Other and further objects of this invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.